Train to make the bullets land where you want and even a hit from the lowly 22LR will kill a person where they stand.

Yes, it's not what you hit with, but rather what you hit. Immediate incapacitation requires a hit to the CNS or a vascular structure that will produce a precipitous drop in blood pressure that results in unconsciousness.

Unfortunately, there are those who'll always be looking for a bullet that produces that mythical "100% one-shot-stop" regardless of what part of the human body it hits. Ammunition design can never compensate for ammunition placement.